Clean up WordPress meta data, like comment and post meta. Don't forget to set your table prefix

cleanup-wordpress-database.sql

-- Clean WordPress Post Meta Data
SELECT * FROM wp_postmeta pm LEFT JOIN wp_posts wp ON wp.ID = pm.post_id WHERE wp.ID IS NULL;
DELETE pm FROM wp_postmeta pm LEFT JOIN wp_posts wp ON wp.ID = pm.post_id WHERE wp.ID IS NULL;

-- Clean WordPress  Comment Meta Data
SELECT * FROM wp_commentmeta WHERE comment_id NOT IN ( SELECT comment_id FROM wp_comments );
DELETE FROM wp_commentmeta WHERE comment_id NOT IN ( SELECT comment_id FROM wp_comments );

SELECT * FROM wp_commentmeta WHERE meta_key LIKE '%akismet%';
DELETE FROM wp_commentmeta WHERE meta_key LIKE '%akismet%';